Are there any boiler experts on here?

[dippingmytoeinagain]

If so, I'd value some advice please.

I have a Worcester Bosch Greenstar 30 DCi Conventional boiler installed in my kitchen. There's a hot water tank in the airing cupboard upstairs, a programable timer in the kitchen and a thermostat in the hall (both Danfoss units).

Over recent months, with increasing frequency, the boiler won't shut off at the end of a programme. Instead it keeps firing up for a few minutes, then shutting off, only to fire up again. This cycle repeats until I lower the output dial from about 5 (the recommended level) to about 1 or 2. Sometimes I have to switch the boiler off in order to stop it. This is becoming the most regular 'fix'. The programmer can be off, the thermostat can be down low and yet the boiler just keeps on firing up.

I've spoken to the company that service it - no ideas from them. I've spoken to Worcester Bosch - again, no ideas, and I've also spoken to a couple of local heating engineers who again are baffled. No-one has been out to do an inspection on it yet, in part because the problem is very intermittent. The boiler is serviced annually and is about 4 years old, although I didn't have it installed - this was done by the previous house owner.

If anyone has any experience of this or any ideas, I would be very, very grateful. Thanks for reading

It might be the 3-port valve. This contains a switch that turns the boiler on (surprisingly). The valve itself is controlled by the room stat and the cylinder stat and indirectly the timer. You would need someone to look at how it is wired and test if the valve is closing correctly and turning off. If so it is not difficult to replace with new.

You might get a clue if the hot water is getting unexpectedly hot (because the cylinder feed is wrongly staying on after reaching temperature).

If it is the PCB in the boiler, someone familiar with that model should know if there is a common fault that could cause it.

I think it is unlikely to be the programmer, but if you change it, Honeywell are better, and you could change to a programmable Honeywell room stat. I prefer wired, because wireless controls sometimes go wrong of their own accord.

Hijacking the thread with another question rather than clog the boards.

Has anyone recently replaced a conventional boiler to a combi?

We have someone (local) giving us a quote this Friday (Good Friday so hoping that's a sign of a hard worker!). We've had a quote from BG and know they are inflated so are trying to get a sense of real costs. We are in London

The system had a power flush 3 months ago (because it conked out) but we are starting renovations now and want to replace the tanks and relocate the boiler to the utility.

Any advice would be greatly appreciated. And suggestions for combi's too please.

how many baths and showers do you have, and how many people are likely to occupy the home?

Thanks, didn't think to put that. One bath and one shower. House is currently a 2 bed, we are extending to a 3 bed.

pigletjohn Thank you everso much for the reply, yes, the hot water does seem hotter than usual when the boiler is stuck on this cycle. I will have another chat with a heating engineer and ask them to come and look at the wiring for the 3 port valve (is this the little grey box which, in my case, is on the pipework in the airing cupboard?)

Thank you again, I really appreciate you taking the time to reply

Probably something like this

Honeywell and Drayton valves usually last very much longer than 4 years.

pigletjohn Yes, that's the fella - the Drayton one - Mid Point Actuator is says on it (it's attached so the writing is upside down, not sure if that is of any relevance to the problem!) and has a very loose 'switch' under it with some markings on the case. Fingers crossed this sorts the problem. Thanks again for the help